1. Field of the Invention
This invention relates to the field of chemical formulations and processes and more specifically to the use of polyalkylene glycols and non-salt polyether amines to agglomerate/coagulate silica particles in aqueous mineral process streams.
2. Background of the Invention
The presence of silica in mineral processing streams is a significant problem in the mineral processing industry. Natural silica as found in minerals has a low aqueous solubility. However when these minerals are digested in strong acids at elevated temperatures, large amounts of silicic acid is released. This silicic acid can then polymerise in solution to form colloidal silica. Such contaminants may cause difficulties in hydrometallurgical processes if not removed. For example, large quantities of silica, which are extracted in acid leaching of ores, form colloidal particles which, although not visible, may flocculate causing problems downstream by depositing on equipment and interfering with solvent extraction by forming “Pickering” emulsions and cloudy effluents. Such particles are generally less than 0.5 microns diameter.
Current methods to remove silica include using conventional filters. Colloidal silica particles will pass through conventional filters and, although membrane filters of appropriate fineness may be used to remove the silica. Given the fine particle size of the silica particles, use of such filters have the disadvantages of significantly increasing process times and expenses.
High molecular weight polyalkylene glycols (of molecular weight of about 1 million) have been used with some success in removing silica by agglomeration. However, such high weight polyoxyethylenes are not readily available and are expensive.
Lower molecular weight polyoxytheylenes, in combination with quaternary amines, have been used in some circumstances to remove silica, as described in Australian Patent No. 640296 which is hereby incorporated by reference. However, this process is not preferable in some circumstances, such as some hard water systems. Also, overtreatment with the strongly cationic quaternary amines may have the opposite effect of redispersing already agglomerated silica. In addition, it appears that the quaternary amines, which are positively charged species that form salts, function as a flocculant agent rather than as a coagulation agent. The term “flocculant agent” means, for the purposes of this application, a material that promotes the clumping of previously agglomerated particulates. Rather, the term “coagulation agent” means a material that promotes the initial agglomeration of individual particulates. Australian Patent No. 640296 supports this contention by reporting that the addition of the quaternary amine (flocculant agent) preferably occurs after the addition of the polyalkylene glycol (coagulation agent) and that reversing this order results in decreased effectiveness. (Page 5, Lines 18-24). Additionally, this patent reports that using quaternary amines generally increases the size of the agglomerated silica particles from less than 0.5 microns, to at least 1.0 microns (Page. 5, Lines 33-37), supporting the contention that the quaternary amine functions as a flocculant agent.
Consequently, there is a need for an improved compositions and methods for the agglomeration and removal of silica from aqueous mineral process streams. Also there is a need for compositions that provide improved coagulation properties.